1. Field of the Invention
The present invention relates to systems and methods for controlling leaf-eating insect populations. More specifically, the present invention relates to methods and systems for controlling gypsy moth populations at the larval and adult stages utilizing a long lasting wax emulsion formulation for the controlled release of a larvicide and a mating disruption pheromone that can be mechanically applied using conventional spray equipment.
2. Background of the Invention
Chemicals secreted externally by an organism to send information to members of the same species, known as pheromones, are used extensively by arthropods to communicate with each other and can be used in strategies for pest management.
The direct management of insect pests using pheromones for mating disruption, or “attract and kill” approaches can provide excellent suppression of key lepidopteran pests in agriculture and forestry. Large-scale implementation projects have yielded significant reductions in pesticide use while maintaining acceptably low crop-damage levels. There are, however, some difficulties with high populations of pests.
The gypsy moth (GM), Lymantria dispar, is one of North America's most devastating forest pests. The species originally evolved in Europe and Asia and has existed there for thousands of years. In either 1868 or 1869, the gypsy moth was accidentally introduced near Boston, Mass. by E. Leopold Trouvelot. About 10 years after this introduction, the first outbreaks began in Trouvelot's neighborhood and in 1890 the state and federal governments began their attempts to eradicate the gypsy moth. These attempts ultimately failed and since that time, the range of the gypsy moth has continued to spread. Every year, isolated populations are discovered beyond the contiguous range of the gypsy moth, but these populations are eradicated or disappear without intervention. It is inevitable that the gypsy moth will continue to expand its range in the future.
The gypsy moth is known to feed on the foliage of hundreds of species of plants in North America but its most common hosts are oaks and aspen. Gypsy moth hosts are located through most of the coterminous United States but the highest concentrations of host trees are in the southern Appalachian Mountains, the Ozark Mountains, and in the northern Lake States. Gypsy moth populations are typically eruptive in North America; in any forest stand densities may fluctuate from near 1 egg mass per hectare to over 1,000 per hectare. When densities reach very high levels, trees may become completely defoliated. Several successive years of defoliation, along with contributions by other biotic and abiotic stress factors, may ultimately result in tree mortality. In most northeastern forests, less than 20% of the trees in a forest will die but occasionally tree mortality may be very heavy.
Because the females of the European gypsy moth form in the United States are unable to fly, natural spread is very limited. An estimated range expansion due to larval dispersal alone is only expected to be about 1.4 miles per year. The higher rate of spread of 13 miles per year that was observed from 1960 to 1990 is most likely the result of introductions that occur when humans accidentally move gypsy moth life stages into the transition or uninfested zones on outdoor household articles, nursery stock, vehicles, and other objects. These life stages establish colonies that reproduce and expand over successive years. Eventually these “spot” infestations coalesce with the continuously infested area, which produces a high rate of spread. A consortium led by the United States Department of Agriculture (USDA) Forest Service is controlling gypsy moth in the expansion front to reduce its rate of spread using management tools that are quite limited in flexibility and longevity.
Following a successful pilot project initiated in 1992, the USDA Forest Service, along with state and federal cooperators, implemented in 1999 the National Slow the Spread (STS) of the gypsy moth project across the 1,200 mile gypsy moth frontier from North Carolina through Minnesota. The goal of the STS project is to use novel integrated pest management (IPM) strategies in order to reduce the rate of gypsy moth spread into uninfested areas. Implementation of STS is expected to decrease the new territory invaded by the gypsy moth each year from 15,600 square miles to 6,000 square miles, protect forests, forest-based industries, urban parks, rural parks, and private property, and avoid at least $22 million per year in damage and management costs. This new IPM strategy is dependent upon intensive monitoring of low moth populations coupled with timely control of growing isolated populations. While traditional approaches to gypsy moth management address potentially defoliating populations occurring in generally infested areas, the STS project focuses on low-level populations in the transition zone between areas considered generally infested and generally uninfested.
The USDA, state and local governments jointly participate in programs to locate and eradicate new gypsy moth populations in currently uninfested areas. The project consists of a coordinated effort by the USDA (Forest Service and Animal and Plant Health Inspection Service (APHIS)) and nine state governments: North Carolina, Virginia, West Virginia, Kentucky, Ohio, Indiana, Illinois, Michigan, and Wisconsin. The annual cost to deploy the approximately 80,000 traps and treat approximately 275,000 acres is under $11 million. The benefits associated with the reduction in the rate of spread outweigh the cost of implementation by an estimated ratio of at least 3 to 1.
Grids of pheromone-baited traps spaced at two kilometer intervals are used for detecting isolated colonies in the transition zone, a band 100 kilometers wide spanning the entire length of the generally infested area in the United States. When moth captures in traps indicate a possible colony, a delimiting grid with 0.5 kilometer intertrap distance is set to delineate the boundary of the colony prior to treatment. This ensures aerial treatments are accurately targeted. Areas to be delimited or treated are initially determined by a computer algorithm designed to analyze moth capture patterns according to project standards and priorities. Then maps of the recommendations are posted on the Internet, which are used by federal and state representatives to begin planning actions that will be taken in the following year. Plans are discussed, prioritized, and finalized at the project level. The finalized plan of action is then compared to the initial computer recommendations to ensure compliance with project standards.
Widespread use of mating disruption, a noninsecticidal treatment, is one of the key elements in the STS project. Mating disruption is based on the application of controlled-release dispensers that emit an insect sex pheromone for several months. The pheromone emitted by the dispensers interferes with the normal mate-searching behavior of males. As a result, females are not mated and lay nonviable eggs.
There are currently two controlled-release products registered with the United States Environmental Protection Agency (EPA) that can be used to disrupt mating between gypsy moths. Disrupt® II is manufactured by Hercon Environmental (Emigsville, Pa., EPA Reg. No. 8730-55). The pheromone is injected between thin sheets of plastic, and then chopped into small pieces ( 1/32× 3/32 inches). Prior to application, the flakes are mixed with a sticker called Gelva (Surface Specialties UCB, Smyrna, Ga.) to ensure they will stick at all levels in the forest canopy where gypsy moths are found. The plastic flakes slowly release the pheromone into the environment over a 2-3 month period. The second is the 3M™ MEC (Microencapsulated) Sprayable Pheromone for gypsy moth manufactured by 3M™ Canada (London, Ontario, EPA Reg. No. 10350-62). The pheromone is encapsulated in small polymer capsules (5-100 μ in diameter) that are suspended in a thick liquid that preserves the formulation. The pheromone starts releasing through the capsule walls soon after the product is applied and continues to release for a period of up to 6 weeks.
Operationally, flakes are typically applied at a rate of 75 g a.i./ha based on the results of dose response studies conducted with ground-applied and aerially-applied disparlure.
As a result of gypsy moth mating disruption tests using hand applied pheromone dispensers positioned at 1.5 meters above the ground, it has been found that mating success in sentinel females was greater at a height of 15-20 meters than at 1.5 meters. Ground-applied pheromone dispensers fail to impact population growth, presumably because the pheromone does not sufficiently penetrate the canopy where mating takes place. Based on these results, it was concluded that pheromone dispensers must be distributed throughout the forest canopy for mating to be disrupted at all heights. This led to the development of equipment suitable for the aerial application of flakes with a sticking agent (sticker). Special pods mounted on each wing of the aircraft mix flakes and sticker just before dispersal through a spinner. It has been found that, using this system in an operational application of flakes with an effective sticker, approximately 25% of the applied flakes were deposited in the upper canopy, 28% in the middle canopy, 25% in the lower canopy, 12% on understory vegetation, and 10% on the ground.
Aerial pheromone application studies established that mating success declined as the application rate was increased from 7.5 to 75 g of disparlure/ha (or 30 g/a). Also, it has been demonstrated that 30 grams per acre suppresses mating in low-density populations. Recent experiments indicated that mating in low-density populations can be suppressed at even lower doses of 15, 6, and 3 grams per acre. Thus, in 2001-02 the recommended dose for the STS project, dealing with low-density populations, was reduced to 15 grams per acre, at a cost of approximately $17 per acre, which compares favorably with alternative treatments such as double applications of B. thuringiensis ($26-$28 per acre) or a single application of diflubenzuron ($12-$15 per acre). The current recommended doses for the STS project are 15 and 6 grams of active ingredient disparlure per acre. When using Hercon's Disrupt® II the recommended 15 grams is equivalent to 85 grams of flake formulation per acre mixed with two fluid ounces of sticker, providing 1 or 2 sticky flakes per square foot of canopy area. When using the 3M's MEC product, the 15 gram dose is equivalent to 2.6 fluid ounces of product mixed with water and applied at a rate of 1 quart per acre.
Mating disruption has shown to be as efficacious in control of isolated gypsy moth colonies as B. thuringiensis treatments, and the scope of its use in the STS project has increased dramatically. Target-specific tactics such as mating disruption will continue to be critical in STS to protect unique habitats and rare, threatened, or endangered species that occur within the project area.
The effectiveness of gypsy moth mating disruption with the current formulations, however, decreases with increasing gypsy moth population density, and there is evidence that the tactic is effective only when moth populations are sparse; which helps to explain the success of mating disruption in the STS program. Mating disruption as it is, however, doesn't seem to be a promising technology to take back the area in the east where the gypsy moth is already established.
Also, the current disparlure formulations are inefficient in their release of pheromone. For example the flake locks the disparlure, consequently more than half of the active ingredient remains unreleased at the end of the period of male moth flight. Only 27-40% of the applied pheromone is released during the period of male moth flight, or within 42 days after application. This indicates that if more efficient controlled-release formulations that dispense most of their pheromone were developed, the result would be a substantial reduction (as much as 60%) of the amount of disparlure applied per treated area without compromising the efficacy of disruption.
The use of new, more efficient formulations, or a reduction in the dose of the existing formulations, could reduce the amount of active ingredient required for control resulting in a reduction in the per acre cost of this control tactic.
Studies of the vertical profile of disparlure after an aerial application to forest canopies indicated that the vertical distribution of disparlure follows the vertical distribution of the dispensers. It follows that, when flakes are applied without sticker and mostly fall to the ground, there should be a lower concentration of disparlure in the canopy than when a sticker is used. The effect of the distribution of aerially applied dispensers on the effectiveness of mating disruption has been investigated. Strong evidence was produced that mating disruption is less effective when flakes are applied without a sticking agent. There is little effect of gypsy moth mating disruption in the canopy after an application of flakes to the forest floor, as would occur if flakes were applied without sticker. The proportion of wild egg masses collected in 1998 with more than 5% fertile eggs was significantly higher under the no-sticking agent treatment.
The problem is that the use of a sticking agent in aerial flake applications not only increases cost of materials, but it also requires the installation of rare, specialized delivery equipment to planes and helicopters. It also causes clogs in the system which results in spotty applications and frequent loss of proper calibration. Furthermore, there are situations in which it might be desirable to apply the pheromone formulation without sticker, such as over residential areas, to avoid damage of personal property (stickem creates a mess where it lands).
The application of Disrupt II requires specialized application equipment because of the glue and because of the large size and irregular shape of the flakes. These rare, special “pods” must be mounted on each wing of the aircraft, so that the flakes and sticker are mixed just before dispersal through a spinner to the forest floor. In addition to restricting application of pheromone to airplanes fitted with such specialized pods, pilots and field personnel complain that clogging of the system is a recurrent problem, resulting in higher than desired variation of MD applications.
Formulations of other materials such as microencapsulated materials, gels or wax emulsions, which can be applied with conventional spray equipment would open up competition among a larger group of aerial applicators and lead to a substantial reduction in application costs and facilitate operations which have to schedule every year the application of pheromone formulations in the more than half a million acres of forest in a short window of time.
Earlier tests involving a polymethacrylate bead or microencapsulated formulations (Decoy GM Beads, Biosys, Palo Alto, Calif.), which can be applied with conventional spray equipment, suggested that the pheromone release profile may be more favorable than that of the flake's, the microcapsules release a higher percentage of the pheromone. However, current tests with the 3M MEC indicated that microencapsulated formulations released pheromone too rapidly to maintain adequate emission rates from the application period throughout the period of male flight.
Treatments prescribed for suppression in areas under the STS program include the use of two biological insecticides, the bacteria Bacillus thuringiensis variety kurstaki (B.t.k) and the gypsy moth nucleopolyhedrosis virus (Gypchek®), and one synthetic chemical insecticide, diflubenzuron (Dimilin®). Here we further suggest the use of Spinosad, an organic insecticide proven to be a highly effective larvicide on Lymantria dispar with extraordinary knockdown activity, as discussed below.
Gypchek®, containing the gypsy moth nucleopolyhedrosis virus is the only available insecticide that is target-specific to the gypsy moth. When gypsy moth larvae ingest the product containing the virus, it invades the gut wall and attacks the tissues, causing death. Gypchek® has been used extensively in the STS program and has not been found to affect any other species but the gypsy moth larvae, both in laboratory and field tests. Gypchek® is not known to have any adverse human health risks. If adequate supplies were available, this would be the best insecticide to use to avoid non-target species impact.
In most STS cases, two applications of Gypchek® are sufficient to achieve defoliation prevention. The typical application rate of Gypchek® is 1011 occlusion bodies/acre. Low-flying aircraft (fixed wing or helicopters) apply this pesticide to tree canopies in separate flights during the 2nd and 3rd larval instars.
B.t.k. is less specific and will affect other lepidopteran (butterfly and moth) larvae that are feeding during the treatment period. It is not known to have significant direct effects on any other orders of animals or plants. These bacteria contain a crystalline structure that when eaten acts as a stomach poison to the larvae of many species of butterfly or moth that feed on treated leaf tissue and get a lethal dose. Only lepidopterans that are feeding during this active period may suffer mortality. The impact is also lessened somewhat when applied in a patchwork fashion to highly infested areas. This allows non-target lepidopterans in adjacent non-treated forests to migrate into treated areas throughout the remainder of the season. In most STS cases, a single application of B.t.k is sufficient to achieve defoliation prevention. Typical application rates of B.t.k. are 36 BIUs/acre. Low-flying aircraft (fixed wing or helicopters) apply this pesticide to tree canopies during the 2nd and 3rd larval instars.
Diflubenzuron is the least specific and potentially most detrimental pesticide of the three recommended by the Forest Service.
Spinosad is a novel, natural insecticide derived from Saccharopolyspora spinosa Mertz & Yao, a new Actinomycetes species isolated from soil sampled at a sugar mill rum still. Spinosad is a mixture of two complex organic molecules, spinosyn A (C41H65NO16) and spinosyn D (C42H67NO16), and it is produced by Dow Agrosciences (DAS). DAS indicates that spinosad is primarily a stomach poison with some contact activity; it has broad-spectrum activity across insect orders, and it is particularly effective against Lepidoptera and Diptera; little or no toxicity to mammalian and avian species; and favorable environmental characteristics. Spinosad has a novel, neurotoxic mode of action which causes rapid paralysis and cessation of feeding. Laboratory and field evaluations indicate that gypsy moth larvae are highly susceptible to spinosad. Bioassays using red oak leaf disks treated with spinosad in a Potter spray tower yielded an LC50 value of 0.0015 mg AI/cm2 (3-day exposure; 13-day evaluation; 2nd instar larvae). Applied to foliage to run-off in the laboratory (potted red oak seedlings) and the field (4 m-tall birch trees), spinosad effectively controlled 2nd instar larvae at concentrations ranging from 3 to 50 mg/liter.
Laboratory studies supported field observations that control was achieved in part by knockdown due to paralysis. In addition, laboratory results demonstrated that crawling contact activity may play an important role in field efficacy as 50% of treated larvae were paralyzed 16 hours after a 2 minute crawling exposure to glass coated with a 4 mg/litre spinosad solution. It has been found that toxicity in the laboratory, and efficacy and persistence in the field, were comparable to those achieved with permethrin. Spinosad at concentrations in the range 3±50 mg/litre applied to run-off will effectively control gypsy moth larvae in ornamental style applications. At these concentrations control was achieved quickly, larval populations were reduced by 95±100%, and residual activity was high. Even an application rate of 0.75 mg/litre eventually resulted in large population reductions. They found that contact with low Spinosad concentrations caused paralysis (by letting larvae crawl on contaminated surfaces for two minutes), rather than rapid mortality, of gypsy moth larvae. Although recovery after exposure by crawling contact activity to low doses may be possible, it is very unlikely that weak larvae falling from trees in the field will survive to mate and reproduce.
The principal reported activity of spinosad in Lepidoptera is caused by ingestion, not contact. Thus the high knockdown effect on gypsy moth larvae following transient contact with spinosad is remarkable.
Gypchek® is preferred over B.t.k. as a treatment option primarily due to its host specificity. However, Gypchek® is available only in limited amounts because of a specialized production process that requires the use of live gypsy moth larvae. Gypchek® supplies are manufactured and distributed by the Forest Service, and no commercial source is yet available. The Forest Service has set a clear priority for the use of Gypchek® in the protection of federally endangered and threatened species and other sensitive areas. Gypchek® has been made available to the STS program, but its future availability remains uncertain.
Pesticides must be applied just after the emergence of the gypsy moth caterpillar in early May. In some areas where the gypsy moth population is high, as indicated by egg mass sizes and numbers, the Forest Service recommends an additional B.t.k. application 5-7 days after the initial treatment to ensure successful population suppression. The short life of Gypchek® also calls for two applications in separate flights during the 2nd and 3rd larval instars.
The larvicidal effect of all formulations mentioned above, Gypcheck, B.t.k., Diflubenzuron, and Spinosad, are severely shortcut if application is followed by rain. The washing of the chemical from the leaves and trunk of the trees by rain drastically decreases the probability of gypsy moth larvae encountering a high enough dose of larvicide for the effect of the contact or stomach poison to take place.
Because of the short life of the current larvicide formulations, timing of the application is everything: low-flying aircraft (fixed wing or helicopters) must apply these pesticides to tree canopies during separate flights during the 2nd and 3rd larval instars.
Enhancement of longevity and rainfastness of these formulations, even if only for two to four months, would make it easier to guarantee that the larvicide would be present in every high-risk-area detected, in anticipation of the larvae hatching from overwintering egg masses. One of the major advantages would be the extension of the window of opportunity for the timing of the sprays, thus easing the scheduling and execution of the larvicidal sprays: planes would be able to, based on each area's egg mass sizes and numbers, start spraying targeted areas weeks, perhaps a month or more in advance, before the larvae emerge.
Based on the considerations above, we believe that Spinosad might be the best candidate larvicide to be formulated with the Specialized Pheromone and Lure Application Technology for Gypsy Moth (SPLAT GM) of the present invention because of the strong knockdown effect on gypsy moth larvae, at low, economically viable doses; it is produced commercially and in large quantities, is labeled organic and registered for “all crops”; and it is a stable molecule (once UV-protected and anchored by SPLAT).
For the suppression of gypsy moth in areas under protection of federally endangered and threatened species act and other sensitive areas the candidate larvicide to be formulated with SPLAT GM could be Gypchek®.